Now you should be in your editor with the disklabel data.
Arrow down to the bottom of the screen.
You should see some sample labels

# EXAMPLE
#a: 4g 0 4.2BSD
#a: * * 4.2BSD

After the last line you will add your SSD setup, see the WARNINGS section of swapcache(8) about leaving room on the drive for proper wear levelling. For the 40GB drive 32GB should be the max size used for the cache.

Add this line.

b: 32g 0 swap

Now save the file.

Adding Disk to fstab

Edit /etc/fstab and comment out any exisiting swap partitions. Just add a # in front of the line.

#/dev/serno/JPC550HN25.s1b none swap sw 0 0

Add your new device to fstab

/dev/ad6s1b none swap sw 0 0

Setting swapcache to start on boot

To enable swapcache on boot edit /etc/sysctl.conf and add

vm.swapcache.read_enable=1
vm.swapcache.meta_enable=1

See swapcache(8) for other sysctl options like vm.swapcache.data_enable